The present invention relates to the assay of zinc protoporphyrin in whole blood and, more particularly, to a reagent that permits the determination of zinc protoporphyrin levels by hematofluorometry without the required oxygenation or re-oxygenation of hemoglobin in intact erythrocytes.
It has been well established that the determination of zinc protoporphyrin is important in the diagnosis and treatment of various diseases and deficiencies. For example, the determination of zinc protoporphyrin in blood is important in detecting iron deficiency, which affects an estimated 20% of the world's population, and in screening lead poisoning, which remains an environmental and occupational hazard. Equally, the determination of zinc protoporphyrin is important and useful in monitoring therapy or treatment for either of the above noted conditions.
For more than 10 years, a common method to screen for chronic lead exposure or iron deficiency has been to measure the zinc protoporphyrin level of whole blood. This has been most often accomplished using an instrument, the hematofluorometer, which is designed for front-surface fluorometry of whole blood. In making measurements, however, if the hemoglobin is not fully oxygenated, the hematofluorometer gives falsely low values due to a spectral shift of the hemoglobin. To overcome this problem, it was necessary in the past to verify that the hemoglobin was fully oxygenated, and this was accomplished by stirring or aeration of the blood specimens followed by three or more successive readings with the fluorometer. If the several readings were substantially identical, this was an indication of fully oxygenated hemoglobin and thus a relatively accurate zinc protoporphyrin level.
As may be appreciated, there are inherent possibilities for error in the aforementioned system. In addition, this approach to oxygenation is time consuming and thus, less economical. Finally, stored or aged blood becomes much more difficult, if not impossible, to fully oxygenate by existing procedures.